Purdue University is leading the next generation of cooling paints with hexagonal boron nitride

Recently, Dr. Xiulin Ruan, a professor of mechanical engineering at Purdue University, developed the world's thinnest and lightest ultra-white paint. This remarkable achievement won the South by Southwest (SXSW) 2023 Innovation Award in Sustainability due to its various potential applications for reducing cooling energy usage. It is especially attractive for automotive and aerospace applications where lightweighting is critical. 

Professor Xiulin Ruan, PhD student Andrea Felicelli, PhD student Ioanna Katsamba, and Professor George Chiu look at hBN-acrylic paint samples in the lab. (photo credit: Purdue University/Jared Pike) 

Compared to the current market offerings, the new paint reflects 97.9% of sunlight, while existing paints that contain TiO2 are only 80-90% efficient and require multiple coats to achieve similar results. With this level of reflectance, the paint can help the surface of buildings, cars, trains or other vehicles remain at 5-6°C below ambient temperature on average. With that degree of cooling, less air conditioning can be used. 

An earlier version of this ultra-white paint used barium sulfate as the active ingredient. By incorporating Saint-Gobain hexagonal boron nitride (hBN) powder, which is roughly half the density of barium sulfate, Ruan's team achieved a much lighter weight product. Additionally, the combination of hBN’s high refractive index and flat, plate-like structure makes it more effective at reflecting light than spherical particles. This allows the coating to work nearly as effectively with a much thinner layer thickness. Coupling the lower density with thinner layers makes this solution 80% lighter than its predecessor, which is particularly advantageous for transportation, especially as electrification becomes increasingly popular. Moreover, the thermal stability of hBN makes it less susceptible to cracking and discoloration in harsh environments.

Purdue University researchers have created a new formula for the world's whitest paint, making it thinner and lighter. The previous iteration (left) required a layer 0.4 millimeters thick to achieve sub-ambient radiant cooling. The new formulation can achieve similar cooling with a layer just 0.15 millimeters thick. This is thin and light enough for its radiant cooling effects to be applied to vehicles like cars, trains and airplanes. (Credit: Purdue University photo/Andrea Felicelli)

Ruan and his lab are working on further improving this paint by making it even thinner and producing it on a commercial scale.
 
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Source: Xiulin Ruan, ruan@purdue.edu
 

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